1. Field of the Invention
The invention relates to a filter device, in particular a liquid filter, such as a urea filter or fuel filter, having a filter element that is disposed in a filter housing, and having a heater for heating a medium flowing through the filter device.
2. Description of the Prior Art
At low operating temperatures, many known filter devices require a heater, since the viscosity of the media to be filtered in them increases at low temperatures, making passage of the medium through the associated filter element more difficult. In diesel fuel filters, for instance, in cold starting of the associated engine, problems can arise if the outdoor temperature is below the so-called CFPP (cold filter plugging point) of the fuel. In urea filters as well, such a heater may be necessary.
The heaters used are embodied as electrical PTC (positive temperature coefficient) heaters, which have automatic regulation and are especially adapted to the heating situation to be brought about. The PTC elements, however, are comparatively expensive to procure and to process.
In some applications of filter devices, their installation space is severely limited. For such applications, in the case of fuel filters, which have a filter housing with a housing cup and a housing cap, it is known to embody the heater in the housing cap or as a heating rod that protrudes into the clean side of the filter device. However, both versions are comparatively complex and expensive and make additional adaptations to the components necessary.